Semiconductor manufacturing and packaging technology has evolved to the point where device packages can include multiple integrated circuit chips in a stacked relationship in order to provide a smaller form factor and higher integration density at the package level. In such packages, the individual chips each include a multitude of signals that are to be externally transferred. Such transfer occurs over a plurality of metal interconnects that distribute signals to an end surface of the chip. The metal interconnects of different chips in the stack are connected according to a number of different techniques.
Mechanical stress can develop between layers of a chip or between adjacent chips of a package. Such stress is typically caused by a mismatch in coefficient of thermal expansion (CTE) between two adjacent layers. In conventional packages, chips are stacked and interconnected using vertical vias that pass through a silicon substrate, insulated from the substrate by a dielectric layer. In this situation, during device fabrication, or later during device operation, heating and cooling processes can cause damage to the via. This is often times due to the CTE mismatch between the layers. For example, silicon has a CTE value of 3, while the dielectric layer can have a CTE value on the order of 50-60; resulting in a large mismatch. To a lesser degree, the metal of the via has a CTE value on the order of 20 as compared to the dielectric layer CTE value of 50-60, resulting in a mismatch. Such mismatch can cause cracking and delamination when subjected to numerous heating and cooling thermal cycles, negatively affecting device yield during manufacture, and device reliability during operation.